The nation's two biggest wireless carriers are going at it like kids in a school yard over which has the most reliable network. AT&T Mobility launched a broadside last week by asserting in a press release and print ad campaign that, "According to independent third-party data, AT&T has the highest success rate for delivering content across nationwide 4G LTE networks."

Verizon fired back with its own ad.

"Most reliable" has long been the keyword in Verizon Wireless ads. But AT&T says "It's time to take another look at your wireless network." The claim in the ad is based "on a comparison of national carriers' average 4G LTE download speeds for Android and Windows smartphones and iPhone 5." For the reliability test, AT&T cited data transfer completion rates on "nationwide 4G LTE network."

'Take Our Word for It'

AT&T won't say who conducted the tests, insisting it was a "well-known" company. "That's not something we're discussing," spokesman Mark Siegel told us Monday. He said the ad will appear in print and online and a radio commercial is also in the works.

The AT&T print ad simply says it is "the nation's fastest and now most reliable network."

Verizon's ad in Monday's Wall Street Journal retorts that while others (keeping AT&T unnamed) "claim" reliability, "to us it's not a hollow claim. Or a slogan. Or a fancy ad campaign."

Verizon has been rated better than AT&T by both Consumer Reports and JD Power and Associates. A March report by JDPA found that Verizon Wireless ranked highest in wireless network quality performance in five regions.

"Whether AT&T can catch Verizon Wireless in perceived network quality superiority is anyone's guess but their overall ranking by region has improved over time," said JDPA wireless industry analyst Kirk D. Parsons. "And as 4G becomes more prevalent, the gap between the two companies should shrink somewhat."

Neil Shah of Strategy Analytics said that reliability is hard to define, subject to market fluctuation. "AT&T is definitely on the right track with respect to ramping up 4G LTE coverage and should catch up with Verizon in [the first quarter of] 2014," Shah said.

Better Backhaul

"Additionally, AT&T is at an advantage here in terms of seamless mobile data and Internet experience as the 'fallback network' is GSM-based HSPA+, which in terms of throughput (especially data) is way faster and [more] reliable than Verizon Wireless CDMA-based EVDO Rev A network. But coverage in some markets could be questionable compared to Verizon Wireless's network."

As far back as late 2010, AT&T blasted Verizon for not investing in its 3G network before shifting to 4G LTE.